Recent air travel incidents involving ice on aircraft wings have underscored the necessity of detecting the presence, depth, and shape of ice on aircraft wings while in flight. It is difficult to see ice or frost (usually clear or whitish) against a light-colored airplane wing from the cockpit, and even if ice is detected visually in flight, it is almost impossible to accurately determine the thickness of the ice and the rate of accumulation.
The main parts of an airplane are the: cockpit, fuselage, wings, powerplant (engines), landing gear, and the empennage. The wings are attached to each side of the fuselage and these are the main lifting surfaces of the airplane. The wing tip is at the end of the airplane furthest from the fuselage. Ailerons are attached to the rear, or trailing, edges of the wings. Wings have a leading edge at the front. The empennage, or tail section, can include a vertical stabilizer (fin), rudder, a horizontal stabilizer and elevator.
The basic problem is that there is no simple, cost-effective system that will warn a pilot when he first encounters icing in flight and once in icing conditions, there is no system to provide feedback to the pilot on the effectiveness of his anti-icing procedures.
Current systems do not provide the depth and shape of the ice accretion on the aircraft. There is no real-time display of the type of icing. Important factors for a pilot to know are: What shape? How much? and Is the ice increasing or decreasing? This is important because ice shape and depth greatly affects aircraft performance and stall speed. For example, ice horns can provide extreme disruption to the airflow over a wing and are often the final icing shape that leads to a stall. Ice horns are ice formations that are formed perpendicular to relative wind. They are created when outward pressure carves ice into two “horns” that disrupt the airflow and decrease the effectiveness of the wing, greatly increasing stall speed.
Different airfoil shapes collect ice differently in common icing scenarios. The aerodynamic response varies with the shape of the ice on an airfoil (wing). Iced wings can stall without warning at a higher speed than clean wings. The amount of aerodynamic degradation depends on: 1) type of ice; 2) amount of ice accumulation; 3) droplet size; 4) airspeed; 5) flap settings; 6) angle of attack; and 7) asymmetric wing loading. A “clean” wing stalls from back to front giving plenty of airframe buffet warning to the pilot, while an “iced” wing stalls from front to back with little or no warning.
Currently, icing is difficult or impossible to detect at night. Large commercial aircraft have wing illumination lights, but the wings are commonly too far behind the cockpit for easy viewing, or the visible portion of the wing is so far away from the cockpit that subtle changes in ice formations are not observable. The presence of ice on the wings is often detected by observing ice on another part of the aircraft, such as a windshield wiper bolt, rather than by visual observation of the wing itself. Visual inspection is unreliable under conditions of limited visibility brought on by fog, falling snow, freezing rain, and/or by darkness.
Therefore, there is a need for a method to detect the presence and accumulation of aircraft surface contaminants such as ice or frost.